The present invention relates generally to scintillation cameras and more particularly to a gamma camera having a radiation absorbing shell of lead, a casing of steel surrounding a scintillation crystal, a plurality of photomultiplier tubes and a collimator.
In the use of a gamma camera for performing tomography, it is important for good resolution that the distance between the camera and the patient is a minimum. Since it is desirable to have the camera field of view centered as close as possible to the area of interest in the head, when a conventional gamma camera is applied to brain tomography, it may be necessary that the camera be entirely outside the patient's shoulders, when it is rotated around the patient. A displacement of the camera upwards from the patient's shoulders so that the camera could be rotated close to the head of the patient would result in only the very topmost part of the head being examined. This is due to the fact that around the central measuring part of the camera there is a border zone which cannot produce exact data, and furthermore, around this border zone there is a thick shell of lead.
The object of the present invention is to improve a gamma camera so that it is not only useful for ordinary tomography, but it is also particularly suitable for brain tomography. According to the invention, this is accomplished by cutting away at least the part of the shell of lead on the side of the camera nearest to the patient and covering that side with a plate of a material with a high radiation absorption capability, such as tungsten. In a particularly advantageous embodiment of the invention, a part of the casing of steel surrounding the scintillation crystal is also cut away.
By this structural change, the distance from the most useful central part of the camera to a physical outer side thereof is reduced sufficiently that the camera can be rotated in the smallest possible circle around the head of the patient while still covering substantially all of the head, so that brain tomography can be performed with maximum quality. Moreover, this is obtained without detracting from the general applicability of the camera for performing tomography. This reduction of the distance of the useful central part of the camera from the outer side thereof is of course greatest in case of a circular camera but is also applicable with other shapes of the camera. The reduction of the distance is obtained by cutting away the thick shell of lead and replacing it by a thinner type of absorbing plate, e.g., tungsten, making sure that the shielding then takes up a minimum of space. When a part of the crystal casing of steel is also cut away, admittedly, a part of the outer border zone surrounding the central detecting zone of the camera is removed, but this will have no adverse affect on the central active zone. Because of the high prices on tungsten and other well-shielding materials, an economic advantage is obtained by providing such materials at only the part of the shielding nearest to the patient while the rest of the shell of lead remains. For aesthetic reasons, however, the entire chordal portion associated with the shell of lead may be cut away and replaced with a plate of tungsten. It is also possible to remove only the lower portion of the camera nearest the patient and to leave the leaded upper part of the shielding remote from the patient, as the upper part of the camera, containing among other things electronic equipment, allows the required reduction of this compartment which is necessitated by the thicker shielding of lead.